Process of preparing wet strength paper containing acrolein polymers



United States Patent 3,317,370 PROCESS 0F PREPARING WET STRENGTH PAPER CONTAINING ACROLEIN POLYMERS George T. Kekish, Chicago, Ill., assignor to Nalco Chemical Company, Chicago, 11]., a corporation of Delaware No Drawing. Filed Sept. 22, 1965, Ser. No. 489,395 4 Claims. (Cl. 162-168) This application is a continuation-in-part of my copending application filed May 16, 1963, having Ser. No. 281,040 and now abandoned.

The instant invention is concerned with additives useful in improving the wet strength characteristics and other properties of paper products, and also describes their method of preparation and employment. More particularly, the invention relates to certain water soluble polymers and copolymers which may be suitably incorporated into paper whereby its wet strength is measurably improved without sacrifice of other desirable prope'rties such as high absorptive capacity.

It is known that the majority of papers produced without benefit of specific additives when subjected to water or even a moist environment have an extremely low wet strength and easily disintegrate or tear upon handling of any severity.

It has been theorized that the low strength of wet papers is a result of a softening of the fibers and consequent reduction of the bond between them. The wetter papers have approximately only 540% of the strength possessed when dry. It is generally thought that in the contacting fibers in a dry sheet of paper there is some small portion of a cellulosic structure held commonly by the fibers. This cellulosic structure is considered hydrophilic or capable of intimate association with water, though not actually soluble therein. The cohesive strength which normally exists when the paper is in the dry state is substantially reduced when contacted with water, whereby the bonding or adhesion effect between the cellulosic fibers is altered. Thus the cementation of fibers is destroyed and the paper as a whole loses its strength. The adhesion or bonding between the individual fibers in contact with each other, which has been developed upon drying the interfelted web from a suspension of water, is reduced to a point whereby the continuous sheet is virtually useless in certain functions involving contact with water.

Prior art attempts to obviate the above problem and measurably increase the wet strength of papers have generally met with success only through means of addition of certain chemical agents to the paper pulp suspension prior to formation of the wet sheet. However, while wet strengths of paper have been increased by such chemical treatment, other subsidiary problems arise with such treatment. For example, in many instances the increase in wet tensile strength property is concurrently accompanied by a corresponding decrease in desired high absorptive capacity. This loss of absorption is generally due to coating of the paper surface by the additive chemical. Yet, when paper is to be used for such purposes as toweling it is essential that both the desiderata of wet strength and adsorptive capacity are present.

Many other problems arise when chemically treating paper pulp to measurably increase wet strength of products therefrom. For example, such treatment also has the effect of decreasing the flexibility of the paper product whereby it cannot be molded or shaped into the desired form. Such paper products are often extremely stiff or hard. Likewise, the treated paper often becomes brittle or abrasive and useless for certain roles such as for hand or face tissues. yOther paper products, while having the desired tensile strength when wet, lack pliability or drapability. Thus, when such paper products are 3,317,370 Patented May 2, 1967 crushed or crumpled, permanent undesirable creases or wrinkles are formed.

In addition to the above problems created by certain chemical additives, there is a tendency for some additives to measurably decrease the porosity and permeability of the paper product to the point where it cannot breathe. Again such characteristic is undesirable in many areas of use.

Certain polymeric substances have been proposed and have found acceptance as wet strength additives. Again, these have certain drawbacks. For example, many further polymerize or react with the fibers of the paper pulp to an undesirable degree upon process heating of the pulp to form a sheet thereof. Thus, an excessive cure can cause many of the above discussed problems. Likewise, a serious problem exists with use of many polymers in that the requisite solubility or compatibility with the aqueous paper pulp is not present. For example, certain unsaturated aldehydes such as acrolein, when polymerized, form water-insoluble masses which can only be incorporated into the pulp after their chemical conversion by reaction with auxiliary chemicals such as sulfur dioxide or alkali metal bisulfites which impart an anionic character to the polymers. These reagents react with the aldehyde groups to form acetals and render the polymeric molecules sufficiently soluble for use as wet strength agents. Also, in this regard use of anionic polymers as wet strength promoters generally requires further addition to the pulp of a retention aid such as alum. Without benefit of this auxiliary chemical only a portion of the polymer is retained on the paper sheet leading to inefiicient promotion of wet strength.

Some effort has been made to overcome the necessity of making further derivatives of unsaturated aldehydes before they can be effectively used as paper additives. For example, US. Patent 2,657,192 effects the polymerization of acrolein in alcohol. Such a process has certain disadvantages in that it must be carried out in the more expensive organic solvents, and the resultant product is only soluble in such organic solvents. Also, since the reaction is carried out in the presence of alcohol there is a tendency to form acetals in situ, and thus lower the consequent molecular weight of the product. It is generally felt that for best effectiveness as a wet strength agent, a relatively high molecular weight polymer is generally needed. I

It would therefore be of benefit to the art if paper wet strength additives could be produced whereby the tensile strength of the paper products is increased when wet without deleteriously affecting the other desirable properties of absorptive capacity, flexibility, pliability, porosity, etc. It would be of a further advantage to the art if watersoluble polymers of unsaturated aldehydes could be synthesized in a one-step process without resort to subsequent derivative modifications. If such aldehyde polymers could be produced which have the requisite water-solubility for direct incorporation into an aqueous paper pulp system, and yet have relatively high molecular weights, thereby giving effective wet strength character to the treated paper, such products would find ready acceptance in the art. Again, if such additives had the effect of imparting wet strength character to paper products even when added to the precursor pulp in relatively small amounts, polymeric substances of this type would be extremely useful. Lastly, if these aldehyde polymers could be so produced whereby they would be effective wet strength agents for a wide variety of paper stocks, a substantial improvement in the art would be realized.

' It therefore becomes an object of the invention to provide chemical compositions useful as paper wet strength additives.

Another object of the invention is to provide a method of greatly increasing the tensile strength of paper products when wetted and to furnish paper articles which concurrently possess other necessary characteristics of flexibility, water absorbency, porosity, drapability, etc.

Yet another object of the invention is to provide interpolymers from unsaturated acrolein monomers, which have no anionic substituents and which may be used directly as water-soluble reaction products.

A specific object of the invention is to provide copolymers and terpolymers of unsaturated aldehydes which are sufficiently water-soluble so as to be directly incorporated into paper pulp slurries without further modification of structure. Special manipulative techniques are disclosed with respect to achieving these water-soluble polymeric species.

And still another object of the invention is to provide cationic derivatives of the above copolymers and terpolymers which are especially useful in treating specific types of paper stock.

A further object of the invention is to provide copolymers and terpolymers of alpha-beta unsaturated aldehyde monomers having no anionic substituents and which have the requisite water solubility, high molecular weight and effectiveness as paper wet strength agents even at relatively low use concentrations and without the use of aluminum salts as a retention device.

Other objects will appear hereinafter.

In accordance with the invention, it has been discovered that a certain class of alpha-beta-unsaturated aldehyde interpolymers are extremely useful in imparting high wet strength to paper products so treated with these additives. In its broadest aspect the invention lies in the discovery of certain new copolymers, terpolymers and cationic derivatives thereof, their method of preparation and the process of employing same in the paper manufacturing art. The interpolymers of the invention have no anionic substituents and contain at least the polymerized monomers of alphabeta-unsaturated aldehydes and nitrogen heterocycles containing an ethylenically unsaturated group capable of interpolymerization with the above aldehydes. For the sake of simplicity and convenience, the polymers of the invention will be listed and discussed according to the various classes which have been synthesized.

WATER-SOLUBLE COPOLYMERS The first class of useful polymeric wet strength additives of the invention are composed of Water-soluble copolymers of an alpha-beta-unsaturated aldehyde and a nitrogen heterocycle containing an ethylenically unsaturated group capable of copolymerization with such aldehydes. These copolymers, as will be discussed in more detail below, may be synthesized by various manipulative techniques so that they are soluble up to about by weight in water or aqueous liquids containing a measurable portion of water. Further, these copolymers contain no anionic substituents. Such copolymers may then be used directly as aqueous reaction products or further diluted prior to actual incorporation with the paper pulp.

The aldehyde monomers useful in the invention may be represented by the general formula:

where R and R may be either hydrogen, lower alkyl radicals or halogen. When the backbone of the aldehyde molecule contains attached thereto an alkyl radical, it is preferred that these radicals contain less than 6 carbon atoms and more preferably 3 carbon atoms or less. Use for alpha beta unsaturated aldehydes may be chosen from among acrolein, alpha methyl acrolein, alphaethyl acrolein, alpha propyl acrolein, alpha isobutyl acrolein, alpha a-myl acrolein, alpha n hexyl acrolein, alpha bromo acrolein, etc. Other representative aldehyde monomers are crotonaldehyde, alphachlorocrotonaldehyde, beta-chlorocrotonaldehyde, alphabromo crotonaldehyde, alpha beta dichlorocrotonaldehyde, alpha beta dimethyl acrolein, alpha methylbeta ethyl acrolein, alpha methyl beta isopropyl acrolein, alpha-ethyl-beta-propyl acrolein, etc.

The other monomeric substance going to make up this class of copolymers comprises a nitrogen heterocycle having externally attached to the ring, an ethylenically unsaturated group capable of copolymerization with the above type aldehydes. Such may be chosen from a wide variety of monomeric substances such as vinyl oxazolidones, vinyl imidazoles, vinyl imidazolines, vinyl pyridines, vinyl pyrrolidones such as N-vinyl pyrrolidones, 2-vinyl pyrrolidone, etc. Other specific nitrogen heterocycles useful as monomeric starting reagents include N- vinyl-5-methyl-2-oxazolidine, N-vinyl-2-oxazolidone, N- vinyl imidazole, N-vinyl-Z-methyl imidazole, 2-vinyl imidazole N-vinyl-3-morpholinone, N-vinyl caprolactam, etc. Preferred among these nitrogen heterocycles are the vinyl pyrrolidones. Excellent wet strength additives have been made in which the starting monomer mixture contains from 10 to mole percent acrolein monomer and 20 to mole percent nitrogen monomer. Preferred mixtures contain 20 to 67 mole percent acrolein monomer and 33 to 80 mole percent nitrogen monomer.

The comonomers may be polymerized by a Wide variety of synthetic techniques including bulk, solution, emulsion, suspension, etc., polymerizations. One preferred method is polymerization by emulsion techniques. In its broadest aspect this procedure involves adding of the two monomers to an aqueous solution containing a catalyst and suitable amount of an emulsifying agent. Preferably, the reaction flask has been previously purged with an inert gas such as nitrogen. Almost any type of known emulsifier may be employed, but preferred are oxyalkylated alkyl phenols, such as the well-known Triton materials, ethylene oxide condensates of fatty acid amides such as Ethomids-IS, O-15 and HT-15, as Well as Arlacel 80 and Span, which are sorbitan monooleates. Other suitable emulsifying agents are sorbitan nono-stearate, sodium dodecyl benzene sulfonate, alu minum stearates, aluminum oleates, etc. Only minute amounts of these emulsifiers are necessary, say from about 10 to about 1000 p.p.m. The concentration of the active monomer ingredients in the reaction mixture may be as low as about 1.0% and as highly concentrated as an emulsion containing 50.0% monomer subject to the later discussed dilution requirement. The reaction itself may be run in the presence of air, but it is preferred that the reaction vessel be first purged with an inert gas such as nitrogen, carbon dioxide, etc, in order to rid the system of oxygen having somewhat of a tendency to inhibit polymerization and provide lower product molecular Weight.

The catalyst that are employed in the process include conventional peroxidic oxidizing agents such as potassium persulfate, hydrogen peroxide, and ammonium persulfate. It is preferred that water-soluble compounds be used for this purpose. The amount of catalyst used in the process can vary from 0.003% to about 0.2% by weight based on the weight of the monomers. The preferred range is from about 0.003% to about 0.05%. In a preferred embodiment, the polymerization action is carried out using a redox type catalytic system. In this method it is particularly preferred to remove oxygen from the system and introduce an inert gas therein in order to permit the catalyst to form free radicals. In a redox system, the catalyst is activated by means of reducing agent which, in the absence of oxygen, immediately produces free radicals without the use of heat. of the reducing agents most commonly used is sodium metabisulfite. Other suitable agents include water-soluble thiosulfates, hydrosulfites, and reducing salts, such as the sulfates of metals which are capable of existing in more than one valent state. The metals include cobalt,

One

iron, nickel and copper. Another excellent reducing agent is silver nitrate. The use of a redox initiator system has several advantages, the most important of which is that it .is possible to carry out the polymerization at lower temperatures since it is not required to decompose the catalyst. The catalyst and the activator may, if desired, be dissolved in a small amount of water and then added to the reaction mixture containing the emulsified monomers. Also, the catalyst initiator may be added directly to the emulsion and dissolved therein with mild agitation.

The polymerization itself is carried out at rather low temperatures, and preferably below about 80 C. More preferably, the reaction is carried out at a temperature range of 2060 C., for a period of time of at least one hour. Excellent polymers have been formed in from about 1 to about 3 hours reaction time.

The water-soluble copolymers of the above discussed type were prepared by the simple expedient of effecting polymerization of the mixture of monomers while keeping the monomer solids content below about by weight during at least /3 of the reaction time and more preferably between /3 and /3 of the time of reaction. Water-soluble copolymers having excellent wet strength activity are prepared by dilution below 10% concentration during the last /3 of the reaction period. It is believed that these are the first acrolein type interpolymers produced directly in a water-soluble state as reaction products without resort to subsequent modification such as by reaction with bis-ulphite salts, sulphur dioxide or interpolymerization with monomers containing anionic groups such as anionic sulfur-containing comonomers.

As stated above, the concentration of monomers at the start of the reaction may be as high as 50%. But during the reaction itself, dilution with water must be effected so that the above requirement of dilution during reaction is met. This additionv of water may be carried in a step-wise manner as by slug feeding or by continuous slow dripping into the reaction media. In any case, all that is essential is that during at least one-third of the reaction time, the concentration of reactants, existing in form of polymer and/ or its parent unpolymerized monomer species, be kept below about 10% by weight solids content. Products synthesized by this method generally have solubility in water up to about 10% by weight.

If one desires that the water-soluble products be kept in an aqueous homogeneous condition for long periods of time, known stabilizers such as hydroquinones and other anti-oxidants may be added in small amounts to the final aqueous product. As little as 0.01% of stabilizer is effective. However, products having excellent longterm stability as homogeneous solutions in water, may be prepared without benefit of stabilizer.

The water-soluble copolymer derivatives prepared as outlined above show excellent activity as wet strength agents without benefit of any additional agent. Due to the fact that these polymers contain no anionic substituents, it is unnecessary to employ aluminum salts to aid in retention. It is believed that these are the first watersoluble acrolein type interpolymers which may be added to the paper pulp slurry without a retention aid such as alum or other aluminum salts and still achieve superior wet strength. It has been discovered that polymers containing even minor amounts of anionic groups or constituents require benefit of retention aids to be effective wet strength agents. The process of the invention is therefore a distinct advance in the art in that extremely efficient results may be obtained with sole use of the defined polymers which should be free of any anionic character.

CATIONIC WATER-SOLUBLE COPOLYMERS These cationic derivatives are easily prepared by reacting any desired amount of water-soluble amine or amine quaternary with the above produced water-soluble copolymers. The cationic reaction is preferably run in about hour to 2 hours at a temperature below 80 C. and

more preferably between 10 and 60 C. These cationic copolymers show particular use in treating pulps which are anionic or neutral in character, such as highly bleached paper pulps. Again, excellent results are shown without the use of aluminum salt.

The amount of amine or amine quaternary reactant added to the water-soluble copolymer may vary considerably. More preferably, the mole ratio of water-soluble copolymer to the amine reactant ranges from 50:1 to 1:1. Most preferably, the mole ratio of copolymer to amine ranges from 25:1 to 5:1.

The amine modifier may be any molecule containing 2 or more amine groups either in the form of the free amine base and/or as quaternary groups. The amines themselves may be primary, secondary or tertiary. Thus, suitable modifiers may be ethylene diamine, diethylene triamine, triethylene tetramine, tetraethylene pentamine or partial or fully quaternized derivatives of any of the foregoing, hydrazines, hydrazides and quaternaries thereof such as betaine hydrazide chloride, N-N-dimet-hylgly cine hydrazide, unsymmetrical dimethyl hydrazides, polymers such as those formed by reaction of urea and polyalkylene polyamines, guanidines, biguanides, guanylureas, mono and polyhydroxy polyamines and quaternaries thereof, etc.

WATER-SOLUBLE TERPOLYMERS Other useful interpolymers of the acrolein type are terpolymers. These are made by polymerizing a mixture containing an alpha-beta-ethylenically unsaturated aldehyde monomer, a nitrogen heterocycle containing an ethylenically unsaturated group and an ethylenically unsaturated monomer containing a non-anionic hydrophilic radical as a side-chain. The first two monomer materials have been discussed in detail above, and need no further elaboration. The third monomer going to make up the useful terpolymers of the invention may be chosen from a wide variety of available materials, with the only requirement being that the monomer contain no anionic substituent. In each case the monomer contains an ethylenically unsaturated group in the backbone of the molecule and a non-anioni-c hydrophilic radical existing as a side-chain oif the backbone.

Useful ethylenically unsaturated monomers containing a non-anionic, that is, a nonionic or cationic hydrophilic or water solubility promoting group, include those in which the hydrophilic group is selected from the class consisting of carboxylic acid amide, hydroxyl, hydroxyl alkyl ether, and the like. Specific monomers include hydroxyethyl acrylate or methacrylate, vinyl acetate, vinyl methyl ether, etc.

The water-soluble terpolymers are prepared in a manner like that used to make the copolymers whose mode of polymerization was described in detail above. Again, such reaction is carried out by maintaining the active solids concentration of the reactants below about 10% by weight during at least /3 of the reaction time. The polymerization is preferably carried out in aqueous media. It has been determined that for best results the proportions of the respective three monomers employed, range in mol percents of from about 10 to about of each monomer.

Likewise, cationic derivatives of the above type terpolymers may be easily prepared in the same manner as discussed above. The cationic derivatives of the water-soluble terpolymers are excellent Wet strength agents used without aluminum salts. As in the case of the cationic copolymers, the cationically modified terpolymers find particular use in promoting the wet-strength of paper derived from alpha-sulfite pulps.

METHOD OF APPLICATION The Water-soluble copolymers, terpolymers and cationic derivatives thereof may be added to any type of paper in order to increase the wet-strength of the subsequently formed paper product. It is greatly preferred however, that when anionic and non-ionic paper pulps are to be treated, the cationic copolymers or terpolymers are employed as treating agents. Such pulps as groundwood, unbleached kraft, unbleached sulfite, unbleached Mitscherlich, semi-bleached kraft, bleached sulfite, alphasulfite, rag, unbleached softwood pulp, bleached hardwood sulfite pulp, or any pulp derived from a mechanical, chemical, or semi-chemical process may be treated with the wet-strength agents of the invention.

The polymers may be added to the pulp either directly as a reaction mass solution or as further diluted solutions, and either via batch or continuous addition. The required amount of treating agent may be added by gravity flow or by means of pumps, preferably, with some type of metering guide. Flow rates for the diluted treating solutions may be controlled with rotometers or other suitable flow measuring devices such as orifices and weirs. Likewise the polymer may be supplied to the pulp in controlled amounts by means of reciprocating, proportioning or gear metering pumps.

The wet strength polymers should for best results be added to the paper stock prior to sheet formation, that is added, to the slush stock at any point from the heater to the headbox or cylinder vat. In this method of application, uniform distribution of the polymer throughout the pulp is achieved, resulting in uniform wet strength of the paper product. The most satisfactory points of addition of the wet strength polymers of the invention are at the beater-s, consistency regulator, Jordan discharge lines, screen, fan pump, cylinder vat or headbox. It has been determined that the copolymers and terpolymers of the invention are strongly attached to the fibers and held by them when the sheet is formed, and are not separated from the fibers by the vigorous conditions of washing which are imposed by sheet formation.

One excellent property of the polymers of the invention used as wet strength additives is that cure of same upon the paper sheet may be effected even at room temperature. Many prior art materials cannot be cured or permanently affixed to the paper sheet without application of heat. Likewise, the polymers of the invention may also be cured at higher temperatures such as the temperature of formation of a paper sheet from a Fourdrinier papermaking machine. Also, even at the relatively high temperature cures, the polymers of the invention do not coat the paper to an extent whereby the water absorbency of the formed paper product is deleteriously affected.

The polymers of the invention may be added to the paper slurry in amounts as low as 0.001% by weight of active polymer based on the bone-dry weight of the paper. More preferably, the polymers are added at an addition level of at least 0.1% by weight based on the fiber weight. As high as 10.0% by weight of polymer may be added. Generally the effectiveness of the wet strength agents of the invention are proportional to the molecular weight as measured by solution viscosity. Therefore, the highly viscous or higher molecular weight materials need to be added in amounts less than those materials which have a relatively lower molecular weight. Generally, the products of the invention have molecular weights of at least 5,000 and more often have molecular weights ranging above 10,000.

By incorporation with the wet strength agents of the invention the wet and consequently dry strengths of a wide variety of paper products are materially increased. The type of paper product which may be beneficiated by increase in wet strength includes tissue paper, photographic paper, wrappings for moist foods, construction papers, map and blueprint papers, paper fabrics, bags. shower shoes, decorative articles, disposable table covers, hand towels, diapers, handkerchiefs, bandages, bed sheets and other paper articles which may take the place of textile fibers, high strength filter paper, cigarette paper, blotting paper, such as desk blotters, tea bag paper, outdoor posters, lens paper, windshield wiping tissue, etc.

It has been noted that when high absorptive capacity is required such as when paper towels and napkins are the paper products treated, these articles have the requisite wet strength, and yet natural absorptive capacity is not materially altered. Also, in addition to achievement of high tensile strength, it is possible by judicious adjustment of quantities of polymer used, to maintain the paper product in the proper flexible and pliable state. Thus, for example, tissues so treated have the requisite wet and dry strength, and nevertheless are soft and pliable with no hint of abrasive action though tear resistance is materially increased. The wet strength agents of the invention also do not affect the porosity of the paper, and no not impart malodors. In addition, the desired body, and properties of moldability, stiffness, resiliency, and folding number, etc., are not impaired by addition of the wet strength agents. Paper products having incorporated therein the cured wet strength agent, may undergo vigorous manipulation under service and exhibit good stretching ability along with the other above desired properties.

The following examples show typical polymer preparations and their effectiveness as wet strength agents. These examples are meant to be illustrative and the invention, of course, is not limited thereto.

Wet strength performance was measured according to the TAPPI Standards and Suggested Methods: T 404 M50 and T 456 M-49.

Dry and wet tensile strengths were determined on a Thwing-Albert Tensile Tester, Model No. 30-LT. The wet strength performance are expressed in terms of percentages and are equal to the wet tensile strength divided by the dry tensile strength.

Example I This example illustrates a typical polymerization carried out so that the copolymer product thereof is soluble in water and particularly soluble in the aqueous reaction media from which it is formed. 45 milliliters of water and 2 millimols of potassium persulfate were placed in a 1 liter, 3 necked flask, arranged with stirrer and thermometer. After purging this flask with nitrogen, 11.1 grams of N-vinyl-2-pyrrolidone and 5.6 grams of distilled acrolein were added, followed by addition of 2 millimols of silver nitrate dissolved in 5 ml. of water. After several minutes of stirring the 2 monomeric reactants together, the temperature rose 5 C. and the liquid reaction mixture became increasingly viscous. 50 ml. of water was then added to the reaction mass. Over a course of 2 hours of reaction time, 350 ml. of additional water were added in incremental additions so that during slightly more than /2' of the reaction time the solids concentration of reacting monomers was less than 10%. The temperature during this time was maintained at between 25 C. and 30 C. At the termination of the polymerization 0.1 gram of hydroquinone was added as a stabilizer. The product was a clear, viscous, aqueous liquid containing 3.58% by weight of dissolved copolymer. This particular product when tested for ability to impart wet strength to products derived from unbleached soft kraft pulp produced a paper product with a 31.4% wet strength. Yet, the excellent wet strength imparted to the paper was achieved by treatment of pulp with polymer as a sole reagent without resort to auxiliary chemicals as alum to aid retention. The water-soluble copolymer was added at a dosage level of 1.0% by weight of active copolymer based on the bone dry weight of the paper fibers.

Example 11 This example is concerned with a preparation of a typical cationic copolymer of the invention. grams of the acrolein-N-vinyl-pyrrolidone copolymer (3.58% concentration) as prepared in Example I were placed in 9 a 250 ml. beaker. 0.15 gram of betaine hydrazide chloride was added to the aqueous copolymer with stirring and with the liquid reaction mixture kept at a tempertaure of 35-40 C. for a period of 30 minutes. This product was 10 Other Water-soluble polymers were also prepared hav-- ing varying ratios of acrolein, and N-vinyl-pyrrolidone. Likewise cationic derivatives of the water-soluble copolymers were prepared. Terpolymers of acrolein-N-vinyl tested on an alpha-sulfite pulp without the use of any pyrrolidone-vinyl-acetate were also prepared in varying aluminum salt. The resultant paper product so treated mol ratios. Some of these were also modified by reacgave a wet strength of 30.4%. In this case the amine tion with a betaine hydrazide chloride amine-quaternary. group reacts with the aldehyde group of the copolymer All of these copolymers and tel-polymers, unmodified or and introduces the quaternary cationic group into the cationically modified, were tested in either alpha-sulfite product. In a comparative test a water-soluble bisulfite pulp or unbleached soft kraft pulp without further addiadduct of polyacrolein, specifically, the sodium bisulfite tion of alum. Wet strength results are presented below addition product of acrolein, when tested for efiectiveness in Table I. The above wet strength additives were added as a wet strength additive on alpha-sulfite pulp gave a at a dosage level of 1.0% by weight based on bone dry paper product having a wet strength of only 10-12%. weight of paper fibers.

TABLE I Wet; Strength, Percent No. Monomers Mol Modified by- Ratio Unbleached Sulfite Pulp-No Pulp Al No Al 1 Acrolciu-NVP 1:3 27.4 2 d0 124 22.2 3 1:2 27.9 4 1:1 31.4 5 1:0.6 32.4 6 120.6 28.8

chloride. 1: l: 1:

1:1:1 Betalne hydrazide 28.5

chloride. 1:0:711 30.4 1:07.1 Betaine hydrazide 31.4

chloride. 1:0.6 1 do 29.2

This wet strength percent was obtained only when alum was also applied to the paper pulp. When no alum was used in conjunction with the bisulfite adduct of polyacrolein a wet strength of only 3% was obtained. The amount of aluminum sulfate added when employed was 3.0% by weight based on the dry weight of the paper fibers.

Example 111 The particular interpolymer produced in this example was a terpolymer of acrolein, N-vinyl-pyrrolidone and vinyl acetate. Into a 2 liter, 3 necked flask arranged with stirring device and thermometer, were added 95 milliliters of water and 0.54 gram of potassium persulfate. The flask was purged with nitrogen and then 18.7 grams of distilled acrolein, 28.7 grams of distilled vinyl acetate and 25.9 grams of N-vinyl-pyrrolidone were added, followed by addition of 0.34 gram of silver nitrate dissolved in 5 ml. of water. After a period of minutes the ternperature slowly rose to a peak of 33 C. and the dilution was then begun slowly. The reaction mixture was diluted over a period of three hours with 1,292 ml. of water in such a manner that the solids concentration of reactants was below 10% during the last 1 /2 hours of reaction time. At the end of the reaction time, the solids content was 3.13% in water. This terpolymer was added at a 1.0% dosage level to unbleached soft kraft pulp and the treated paper product was then measured for wet strength. This product had a wet strength of 30.4%.

Example IV This example illustrates preparation of a cationic terpolymer. ple III (3.13% by weight in aqueous solution) was added 0.09 gram of betaine hydrazide chloride. The cationic material and terpolymer'were stirred for minutes at 4-0 C. An alpha-sulfite pulp treated with 1.0% by weight of the above cationic terpolymer when formed into a sheeted paper product had a 31.4% wet strength.

To 297. 0 grams of the terpolymer of Examthe type listed above without departing from the scope of the invention.

It has been shown that the novel copolymers and terpolymers described herein are highly elfective as wetstren gth agents in the absence of alum. It should be further noted however that the novel treating agents are equally effective in systems wherein aluminum salts are normally present, such as where alum is used to retain rosin size or other materials.

In addition to their primary utility as wet-strength agents the copolymer-s, modified and unmodified, and cationically modified 0r unreacted terpolymers may be used as additives in a number of processes or employed per se to produce a variety of manufactured articles. For example, the aqueous solutions of polymers may be cast or spun into shaped articles, sheets, films, wrapping tissues, tubing, filaments, yarns, threads, etc. For example, aqueous or alcoholic solutions of the polymers of the invention, by evaporative techniques may be shaped into any desired industrial article. Likewise, the polymers may be used in coating, finishing, casting or molding for adhesion or lamination. Specifically, they may be used as adhesives for cellophane, paper, cloth, etc., as finishes for fabrics, as permanent sizes for yarns, as protective water resistant coverings, for use as sausage casings, as dye intermediates, as filament film formers, etc. The polymers may also find excellent use as anchoring agents for natural and synthetic filaments, films and artificial leather. They may also be used to finish and impregnate or coat by surface modification or other manipulative techniques, a number of industrial and commercial articles. The

versatility of the polymers of the invention in that they may be suitably cured both at room temperature and above, help them find use in many of the above stated processes.

The invention is hereby claimed as follows:

1. The process of treating paper to increase the strength thereof without rendering the same impermeable to Water which comprises adding to an aqueous suspension of cellulosic paper fibers from 0.01 to 10.0%, based on the bone dry weight of the fiber, of a water-soluble wet strength agent whereby said agent is adsorbed upon said fibers, forming the thus treated fibers into a matted product by draining the suspended water therefrom, and drying said matted product, said wet strength agent consisting of the water-soluble product of polymerization of a mixture of monomers consisting of from to 80 mole percent of an alpha-beta-ethylenically unsaturated aldehyde having the following formula:

where R and R are selected from the group consisting of halogen, lower alkyl radicals and hydrogen, and from to 90 mole percent of a reactant selected from the group consisting of (A) a nitrogen heterocycle containing an ethylenically unsaturated group capable of copolymerization with said aldehyde and (B) mixtures of said nitrogen heterocycle and another ethylenically unsaturated monomer having no anionic substituents and containing a hydrophilic radical as a side chain and capable of terpolymerization with said aldehyde and said nitrogen heterocycle such that each monomer is present in an amount ranging from 10 to 70 mole percent, said polymerization product being prepared whereby it is soluble in aqueous liquids up to about 10% by weight of solids by carrying out said polymerization as a dilute aqueous reaction mixture containing below about 10% by weight of said mixture of monomers during at least /3 the period of said polymerization reaction.

2. The process of treating paper to increase the strength thereof Without rendering the same impermeable to water which comprises adding to an aqueous suspension of cellulosic fibers from 0.01 to 10% based on the bone dry weight of fiber, of a water-soluble wet strength agent whereby said agent is adsorbed upon said fibers, forming the thus treated fibers into a matted product by draining the suspended water therefrom, and curing said matted product, said wet strength agent consisting of the water-soluble product of polymerization of a mixture of monomers consisting of from 20 to 67 mole percent of acrolein, and from 33-80 mole percent of a reactant selected from the group consisting of (A) vinyl-pyrrolidone and (B) mixtures of vinyl-pyrrolidone and another ethyenically unsaturated compound having no anionic substituents and containing a hydrophilic radical as a side chain and capable of terpolymerization with said acrolein and said vinyl-pyrrolidone such that each monomer is present in an amount ranging from 10 to 70 mole percent, said polymerization product being prepared whereby it is soluble in aqueous liquids up to about 10% by weight of solids by carrying out said polymerization as a dilute aqueous reaction mixture containing below about 10% by weight of said mixture of monomers during at least /3 the period of said polymerization reaction.

3. The process of treating paper to increase the strength thereof without rendering the same impermeable to water which comprises adding to an aqueous suspension of cellulosic paper fibers from 0.01 to 10. 0% based on the bone dry weight of the fibers, of a water-soluble wet strength agent whereby said agent is adsorbed upon said fibers, forming the thus treated fibers into a matted product by draining the suspended waters therefrom, and curing said matted product, said wet strength agent consisting of the water-soluble product of polymerization of a mixture of monomers consisting of from 10 to mole percent of an alpha-beta-ethylenically unsaturated aldehyde having the following formula:

R1 R2CH=( JCI-IO where R and R are selected from the group consisting of halogen, lower alkyl radicals and hydrogen, and from 20 to mole percent of a reactant selected from the group consisting of (A) a nitrogen heterocycle containing an ethylenically unsaturated group capable of copolymerization with said aldehyde and (B) mixtures of said nitrogen heterocycle and another ethylenically unsaturated compound having no anionic substituents and containing a hydrophilic radical as a side chain and capable of terpolyme-rization with said aldehyde and said nitrogen heterocycle such that each monomer is present in an amount ranging from 10 to 70 mole percent, said polymerization product being prepared whereby it is soluble in aqueous liquids up to about 10% by weight of solids by carrying out said polymerization as a dilute aqueous reaction mixture containing about 10% by weight of said mixture of monomers during at least of the period of said polymerization reaction, said polymerization product being further characterized as having been treated with an amine capable of reacting with said polymerization product whereby said polymerization product is rendered substantially cationic.

4. The process of treating paper to increase the strength thereof without rendering the same impermeable to water which comprises adding to an aqueous suspension of cellulosic fibers from 0.01 to 10.0 percent, based on the bone dry weight of fibers, of a water-soluble wet strength agent whereby said agent is adsorbed upon said fibers, forming the thus treated fibers into a matted product by draining the suspended water therefrom, and curing said matted product, said wet strength agent consisting of the watersoluble product of polymerization of a mixture of monomers consisting of from 20 to 67 mole percent of acrolein and from 33 to 80 mole percent of a reactant selected from the group consisting of (A) vinyl-pyrrolidone and (B) mixtures of vinyl-pyrrolidone and another ethylenically unsaturated monomer having no anionic substituents and containing a hydrophilic radical as a side chain and capable of terpolymerization with said aldehyde and said vinyl-pyrrolidone such that each monomer is present in an amount ranging from 10 to 70 mole percent, said polymerization product being prepared whereby it is soluble in aqueous liquids up to about 10% by weight of solids by carrying out said polymerization as a dilute aqueous reaction mixture containing below about 10% by weight of said mixture of monomers during at least /2, the period of said polymerization reaction, said polymerization product being further characterized as having been treated with an amine capable of reacting with said polymerization product whereby said polymerization product is rendered substantially cationic.

References Cited by the Examiner UNITED STATES PATENTS 2,771,362 11/1956 Moser et al 162-168 3,012,998 12/1961 Wishman et al 260-805 3,056,819 9/1962 Carlin 260-805 3,079,296 2/1963 Houfi et al. 162-168 3,093,506 6/1963 Tsatsos 162-168 X 3,121,700 2/1964 Bergman 162-168 X 3,129,195 4/1964 June et al 260-805 X DONALL H. SYLVESTER, Primary Examiner.

S. LEON BASHORE, Examiner. 

1. THE PROCESS OF TREATING PAPER TO INCREASE THE STRENGTH THEREOF WITHOUT RENDERING THE SAME IMPERMEABLE TO WATER WHICH COMPRISES ADDING TO AN AQUEOUS SUSPENSION OF CELLULOSIC PAPER FIBERS FROM 0.01 TO 10.0%, BASED ON THE BONE DRY WEIGHT OF THE FIBER, OF A WATER-SOLUBLE WET STRENGTH AGENT WHEREBY SAID AGENT IS ADSORBED UPON SAID FIBERS, FORMING THE THUS TREATED FIBERS INTO A MATTED PRODUCT BY DRAINING THE SUSPENDED WATER THEREFROM, AND DRYING SAID MATTED PRODUCT, SAID WET STRENGTH AGENT CONSISTING OF THE WATER-SOLUBLE PRODUCTO OF POLYMERIZATION OF A MIXTURE OF MONOMERS CONSISTING OF FROM 10 TO 80 MOLE PERCENT OF AN ALPHA-BETA-ETHYLENICALLY UNSATURATED ALDEHYDE HAVING THE FOLLOWING FORMULA: 